This invention relates to a system for spray coating substrates, such as preformed plastic containers, with a coating material to form on drying a film on the containers. For example, this invention is applicable to coating polyethylene terephthalate bottles with a copolymer of vinylidene chloride to provide the bottles with a gas barrier coating. More particularly, a coating booth containing conventional airless spray equipment and an oven are employed to provide the surface of a continuously moving series of plastic containers, for example, with a spray coating wherein the flow of coating material to the coating booth is controlled, the airborne overspray contained and captured and the liquid overspray recovered and recycled.
In one particular process to which the present invention is applicable plastic containers for beverages made of polyethylene terephthalate (commonly referred to as "PET" bottles or containers) are coated with a vinylidene chloride (commonly referred to as "PVDC") gas barrier coating. This process is carried out by spray impacting a stream of an aqueous dispersion of film-forming polymer particles onto the substrate surface to form a gel layer having the polymer in the continuous phase of the layer. The process provides initially a wet uniform coating of the substrate which coating is then dried completely coalescing the material into a polymer film.
In this process, it is necessary to continuously deliver aqueous coating material to the spray nozzles for the coating of bottles continuously passing through the spray coating booth, to control the airborne aqueous overspray to prevent its release to the atmosphere while containing polymer particles, and to move the bottles between the spray coating booth and the drying oven for drying the wet coating.